HIV infection of adolescents remains a significant problem in the U.S. and other industrialized nations. Worldwide, half of all newly infected persons are between the ages of 15 and 24 years. Despite considerable progress in decreasing perinatal transmission of HIV, there has been little impact on the number of newly infected adolescents in the U.S. and the number of youth infected is to a large extent unknown. Identification of HIV infected adolescents is of particular importance and an even greater challenge in San Diego, a city that borders on Mexico and has the most frequently crossed international border in the world. The UCSD Mother-Child- Adolescent HIV Program has made considerable progress in the development of a comprehensive infrastructure for the identification, care and research participation of HIV infected pregnant women, children and adolescents. The goal of this application is to expand the capacity of the UCSD Mother-Child-Adolescent HIV Program to participate in research directed toward behavioral, preventive, therapeutic and pathogenetic evaluation of HIV infected and at-risk adolescents through participation in the Adolescent Medicine Trials Network (ATN). The two major specific aims of this proposal are: 1) To extend the infrastructure in San Diego in order to expand the capacity of the UCSD Mother-Child-Adolescent Program to contribute significantly to all aspects of the ATN agenda; and 2) To help develop and implement studies within the ATN designed to: a)address behavioral, immunization and therapeutic strategies for the prevention of HIV infection of at-risk adolescents; b)examine behavioral, nutritional and treatment interventions to preserve health of adolescents with asymptomatic HIV infection; and c) examine behavioral, nutritional and treatment interventions to improve and sustain health of adolescents with symptomatic or immunologic impairment associated with their HIV infection. The UCSD Mother-Child-Adolescent Program is committed to participate in all aspects of the development of clinical trials for HIV-infected and at-risk adolescents. The experience of our team in HIV care, clinical trials and laboratory studies, we believe, will enable our group to make a significant contribution to the success of the ATN.